The present invention generally relates to inkjet and other types of printers and more particularly, to a system and method for producing print masks to eliminate step advance and swath height error banding.
Inkjet printers print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more print cartridges each having a printhead with a nozzle member having ink ejecting nozzles. The carriage traverses over the surface of the print medium. An ink supply, such as an ink reservoir, supplies ink to the nozzles. The nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller. The timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
To complete a full line, the print head passes a specified number of times in a single or multi pass pattern. This multiple pass way of printing is called a printmode. The print mode may have a number of parameters; the number of passes required to fill an area, and the position of the ink droplets at every pass. To define this feature, a matrix is created that defines each position of each pass in which a drop may print. The matrix is called the printmode mask.
Lines, text and graphics are normally printed with all nozzles aligned in the horizontal or scan axis. Defects, including tails, spray drops and spear drops, can result in rough edges, vertical lines, horizontal lines, banding, and changes in hues on the print media. These defects may be due to a number of factors including nozzle alignment, nozzle outs, firing frequency, pen noise, print media advance, or swath height error.
The pattern on the print media is altered due to step advance errors. A large step advance error would increase the probability of banding. In a multiple pass mode the effects would be for more clearly defined bands representing areas of ink overlap from each pass between areas of ink overlay without ink from one or more passes of the printhead. In the case of a smaller step advance errors the area of ink overlap on the print media for all passes of the printhead would increase, while the areas which do not have ink from one or more passes of the printhead would be less. In this case the areas of light streaking would be narrower but would occur more frequently.
A further challenge in assuring print quality is the reduction or compensation for swath height error (SHE). SHE may be produced from mechanical, electrical, or other sources that result in dot placement artifacts in the paper axis during printing. Inkjet printers have used a variety of methods to compensate for artifacts in the scan axis, however, correction for artifacts in the paper axis have been limited to adjustments of the media advance. Therefore, what is needed is a system and method to solve these problems.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a system and method for producing print masks to reduce the effects of step advance and swath height error banding.
The printing system of the present invention includes a printhead assembly and an ink supply for printing ink on print media. The printhead assembly includes a printhead body, ink channels, a substrate, such as a semiconductor wafer, a nozzle member and a barrier layer located between the wafer and nozzle member. The printhead has a controller, which can be firmware, software or any suitable processor that can control the ejection of ink from the plural nozzles. The controller can be defined in the integrated circuit as receiving data stored in the data in the buffer memory, assigning primitive addresses in the heater array from the data, and determining the firing pulse rate of the heater elements in the heater array. The controller can be created by any suitable integrated circuit manufacturing or programming process.
The controller determines the firing order of the nozzles in a single or multiple swath with particular reference to a probabilistic print mask generator. The generator functions to firstly calculate the ramp height on a formula to include pen height, data resolution, the number of passes and the pen nozzle resolution. Secondly, taking the ramp height into consideration, the controller allocates on a random basis from the print mask, the firing of nozzles, so that the ramp may begin at zero, although other values may be incorporated to preserve the reliability of the pen, and ends at the ramp height. The system increases the firing rate for centrally located nozzles so that the total ink per unit area of media is equal to that of a conventional print pass. The feature of this system is that swath height error and step advance error effects on the printed image are decreased.